Preheating is required for plated parts, regardless of material, as long as the workpiece is large, because the hard chrome plating time is longer, the plating layer is thicker, the internal stress is large and the hardness is high, and the difference between the coefficient of thermal expansion of the base metal and the chrome is large.
Author: Anna
Precautions for hard chrome plating
①Preheating is required for plated parts, regardless of material, as long as the workpiece is large, because the hard chrome plating time is longer, the plating layer is thicker, the internal stress is large and the hardness is high, and the difference between the coefficient of thermal expansion of the base metal and the chrome is large. If you do not preheat the application of plating, the base metal is susceptible to thermal expansion and produce “storm skin” phenomenon, preheating time according to the size of the workpiece.
② Hanging fixtures with materials must not dissolve in the hot chromic acid solution, and other chemical reactions do not occur. Fixture should also have a sufficient cross-sectional area, and good contact with conductive parts. Otherwise, due to high current, the slot voltage rises, localized overheating.
Should be in accordance with the conductivity of various materials to select the cross-sectional area of the fixture, a few common materials allow the use of current: copper - 3A / mm2, brass - 2.53A / mm2, steel - 2A / mm2. Fixture structure should try to use the welding form of connection; fixture non-working part of the application of PVC plastic cloth or coated with acid-resistant adhesive insulation.
③ Mounting should be considered to facilitate the escape of gas, to prevent the formation of “gas pockets”, resulting in no local plating or uneven thickness of the plating.
④ Complex parts should be chromium-plated with elephant-shaped anode, and the ends of cylindrical parts should be protected with cathode to avoid burning at both ends and thin plating in the middle; parts with corners and tips can be shielded with metal wires.
⑤ In order to improve the bonding force of the plating layer, anti-electricity, high-current impact and step feeding can be carried out. The time of counter-electricity is 0.5~3min, the cathode current density is 30~40A/dm2, the high current impact is 80~120A/dm2, the time is l~3min.
⑥ For steel parts that are easy to precipitate hydrogen, dehydrogenation should be carried out after plating.